Processes

Processes#

Processes define the chemical and physical transformations of species concentrations. Each process provides forcing (ODE right-hand side) and Jacobian contributions to the solver.

DissolvedReversibleReaction#

Equilibrium reactions within a condensed phase:

\[\text{Reactants} \rightleftharpoons \text{Products}\]

with \(K_\text{eq} = k_f / k_r\).

#include <miam/miam.hpp>

auto h2o_dissociation = DissolvedReversibleReactionBuilder()
  .SetPhase(aqueous_phase)
  .SetReactants({ h2o })
  .SetProducts({ ohm, hp })
  .SetSolvent(h2o)
  .SetEquilibriumConstant(EquilibriumConstant(
      { .A_ = 1.14e-2, .C_ = 2300.0, .T0_ = 298.15 }))
  .SetReverseRateConstant(ArrheniusRateConstantParameters(
      { .A_ = 1.4e11, .C_ = 5.1e4 }))
  .Build();

Builder methods#

Method

Description

SetPhase(phase)

The condensed phase where the reaction occurs

SetReactants(species_list)

Reactant species

SetProducts(species_list)

Product species

SetSolvent(species)

Solvent species (concentration used for activity)

SetEquilibriumConstant(obj)

Temperature-dependent \(K_\text{eq}(T)\)

SetForwardRateConstant(obj)

Explicit \(k_f(T)\) (alternative to equilibrium constant)

SetReverseRateConstant(obj)

Explicit \(k_r(T)\)

If both SetEquilibriumConstant and SetReverseRateConstant are provided, the forward rate constant is computed as \(k_f = K_\text{eq} \cdot k_r\).

This process does not require aerosol properties.

HenryLawPhaseTransfer#

Gas-condensed phase mass transfer governed by Henry’s Law:

\[\text{A(gas)} \rightleftharpoons \text{A(condensed)}\]
#include <miam/miam.hpp>
#include <miam/processes/constants/henrys_law_constant.hpp>

auto transfer = HenryLawPhaseTransferBuilder()
  .SetCondensedPhase(aqueous_phase)
  .SetGasSpecies(A_gas)
  .SetCondensedSpecies(A_aq)
  .SetSolvent(H2O)
  .SetHenrysLawConstant(HenrysLawConstant(
      { .HLC_ref_ = 3.4e-2, .C_ = 2400.0, .T0_ = 298.15 }))
  .SetDiffusionCoefficient(1.5e-5)    // m2 s-1
  .SetAccommodationCoefficient(0.05)  // dimensionless
  .Build();

Builder methods#

Method

Description

SetCondensedPhase(phase)

Target condensed phase

SetGasSpecies(species)

Gas-phase species (must carry molecular weight)

SetCondensedSpecies(species)

Condensed-phase solute species (must carry molecular weight and density)

SetSolvent(species)

Solvent species (must carry molecular weight and density)

SetHenrysLawConstant(obj)

Temperature-dependent HLC: \(H(T) = H_\text{ref} \exp(C(1/T - 1/T_0))\)

SetDiffusionCoefficient(D_g)

Gas-phase diffusion coefficient [m² s⁻¹]

SetAccommodationCoefficient(α)

Mass accommodation coefficient [0–1]

This process requires three aerosol properties from the representation: effective radius, number concentration, and phase volume fraction. These are provided automatically by the Model.

See Henry’s Law Phase Transfer for the full equation set and Jacobian derivations.

Rate Constants#

EquilibriumConstant#

Temperature-dependent equilibrium constant:

\[K_\text{eq}(T) = A \cdot \exp\!\left( C \left( \frac{1}{T_0} - \frac{1}{T} \right) \right)\]
EquilibriumConstant keq(
    { .A_ = 1.14e-2, .C_ = 2300.0, .T0_ = 298.15 });

double value = keq.Calculate(conditions);

HenrysLawConstant#

Temperature-dependent Henry’s Law constant:

\[H(T) = H_\text{ref} \cdot \exp\!\left( C \left( \frac{1}{T} - \frac{1}{T_0} \right) \right)\]
HenrysLawConstant hlc(
    { .HLC_ref_ = 3.4e-2, .C_ = 2400.0, .T0_ = 298.15 });

double value = hlc.Calculate(conditions);  // mol m-3 Pa-1

Adding Processes to a Model#

auto model = Model{
  .name_ = "AEROSOL",
  .representations_ = { droplets, dust }
};

// Add multiple processes at once
model.AddProcesses({ h2o_dissociation, co2_hydration, transfer });

AddProcesses assigns each process a unique UUID (via CopyWithNewUuid) so that the same process definition can be reused across modes without state parameter name collisions.